(4) Types of Experiments

• all experiments involve a change in an IV with the researcher recording/ measuring the subsequent effects on the variable
• how the IV changes and under what circumstances varies from different types o experiments
• the four different types of experiments are :

  • laboratory experiments
  • field experiments
  • natural experiments
  • quasi experiments
• Laboratory Experiments :

  • conducted in highly controlled environments
  • not always conducted in a lab - could be in a classroom where conditions are well controlled
• EVALUATION of Laboratory Experiments

  Strengths :

  • high control over extraneous variables - so researcher can ensure the effect on the DV are a result of the manipulation of the IV
  • high internal validity - cause and effect relationships can be established (main aim of psychology)
  • replication more possible due to high levels of control - ensures new extraneous variables are not introduced when repeating experiments
  • standardised procedures used - structuralism
  • replications of a study determines if findings are valid or one off - reliable results ?
• EVALUATION of Laboratory Experiments

  Limitations :

  • lacks generalisability : lab environment may be artificial and not like everyday life - participants behave unnaturally/ unusually due to unfamiliar context of experiment so behaviour cannot always be generalised beyond research setting (low external/ ecological validity)
  • low mundane realism/ ecological validity - may not represent real life
  • demand characteristics - participants aware they are being tested in a lab experiment (may not know why) - cause unnatural behaviour so affects DV
• Field Experiments :

  • the IV is manipulated in a natural way
  • in a more everyday setting - people don't know they're part of it
  • is not necessarily in a field
• EVALUATION of Field Experiment

  Strength :

  • higher mundane realism than lab experiments - the environment is more natural (usually in leaf life setting)
  • may produce behaviour that is more valid and authentic
  • natural behaviour because participants may be unaware they are being studied - high external validity
• EVALUATION of Field Experiments

  Limitations :

  • loss of control of extraneous variables
  • difficult to establish cause and effect relationship between IV and DV
  • precise replication is often not possible
  • Ethical issues : participants unaware they are being studied - cannot consent to being studied - invasion of privacy
• Natural Experiments :

  • researcher takes advantage of pre existing independent variables
  • natural : variable would have changed even if the experimenter was not interested
  • the IV is whats natural, not the setting - participants may be tested in a lab
  • the setting is natural
• EVALUATION of Natural Experiment

  Strength :

  • provide opportunities for research that may not otherwise be taken for practical or ethical reasons
  • high external validity - involve the study of real life issues and problems as they happen (eg effects of a natural disaster on stress levels)
  • eg twin studies/ adoption studies
• EVALUATION of Natural Experiments

  Limitations :

  • naturally occurring event may happen very rarely : reduces opportunities for research - limits scope for generalising findings to other similar situations
  • participants may not be randomly allocated to experimental conditions : means researcher might be less sure whether the IV affected the DV
• Participant variables = individual differences
• Institutionalised Romanian Orphans - nature vs nurture (upbringing)
• Quasi Experiment :

  • IV is based on an existing difference between people (eg age or gender)
  • no one has manipulated this variable - it simply exists
  • its either you have a characteristic or you don't have a characteristic
• EVALUATION of Quasi Experiment

  Strength :

  • carried out under controlled ocnditions
  • share the same strength as lab experiments :
  • high control of extraneous variables
  • high internal validity
  • replication possible - reliable so valid
• EVALUATION of Quasi Experiment

  Limitations :

  • cannot randomly allocate participants to conditions - confounding variables
  • participant variables